The present invention relates to the art of machining workpieces by stock removal and, more particularly, to improvements in a milling apparatus for producing radial geometries.
Radial grooves are used, for example, in the manufacture and assembly of aircraft turbine engines. More particularly in this respect, turbine engines generally have a series of round rings comprised of a group of radial segments that are held in the ring configuration by hooks utilizing radial grooves machined into the segments. Machining of the radial grooves presents a manufacturing challenge due to the tough and expensive alloys that are used in the aircraft industry, as well as the close tolerances required for associated components.
Conventional methods of producing the radial grooves typically require a fixture that holds a quantity of workpiece segments in a ring configuration. The assembly of the workpiece segments must duplicate the diameter that the parts create, for example, in the assembled turbine engine. The current machining method utilizes a conventional vertical turret lathe to machine the radial grooves once all of the workpiece segments are located in the ring configuration. Vertical turret lathes incorporate a cutting tool in a vertical spindle having a fixed axis of rotation, and the workpieces are mounted on a table or base which is rotated relative to the cutting tool for machining of the workpieces by the stationary cutting tool. The disadvantages of using a vertical turret lathe include high fixture costs and the risk of damaging an entire set of parts if the operator and/or lathe makes a dimensional error. Additionally, vertical turret lathes are a less rigid style of milling apparatus, and are limited due to the machine tool spindle accommodating only one cutting tool. Consequently, there remains a need for a milling apparatus for producing radial geometry which overcomes the aforementioned problems and limitations.
In accordance with the present invention, an improved apparatus for the machining of workpieces by stock removal is provided by which the foregoing and other disadvantages and problems with lathes and millers heretofore available are overcome orminimized. More particularly in accordance with the present invention, apparatus is provided which has a radial motion capability combined with machine feed rates and variable speed to create a shaping action that produces grooves of varying radii and radial geometry in segment shaped workpieces. The present invention includes a machine base equipped with a milling table, a workpiece holding fixture, a milling assembly, and a milling guide. The milling guide, in accordance with the invention, establishes a point of rotation for the milling assembly. The milling table includes a carriage mounted thereon with a series of locating or clamping holes machined into its upper surface starting a few inches from the point of rotation of the milling guide and extending outward which allows progressively larger radii to be created depending on the location of the workpiece holding fixture relative to the point of rotation. In one embodiment, the milling table is movable in x and y axes within a horizontal plane. The workpiece holding fixture mounts the segment shaped workpiece to the carriage. As a result of the simplified workpiece fixture, the mounting and machining steps reduce the process time of a workpiece between its introduction to the workpiece fixture and its completion in the finished state. The milling guide is mounted on the milling table and is pivotal about and vertically adjustable along a z axis orthogonal to the horizontal machining plane. The milling guide includes a radial arm which is connected to the milling assembly. The milling assembly includes a base unit for securing the tool holding member which secures the cutting tool. The dimensions of the cutting tool and the vertical feed of the milling assembly, control the width and depth of the groove, respectively. The cutting tool can also be adjusted by means of rotating the base unit of the milling assembly for radial location to produce exact radii in parts that are being shaped to a specific print requirement. The milling assembly and the milling table are independently supported. A control device such as a computer numerically controlled (CNC) controller is used for coordinating the movements of the milling table and the milling assembly to machine a radial groove in the workpiece.
In contrast to the known state of the art, each workpiece segment is machined independently which reduces the time and expense for the fixture arrangement, and also eliminates the risk of damaging an entire set of parts if there is a dimensional or operator error. It will be appreciated that the invention can facilitate a machining cell created to take advantage of a one workpiece flow system.
The workpiece fixture clamps the workpiece to the carriage. A radial arm connects the milling assembly to the milling guide. The milling guide""s pivotal axis is positioned at a preset location relative to the workpiece which is fixedly attached to the carriage by the fixture arrangement. The cutting tool or tools are secured to the milling assembly""s base unit which has an independent axis of rotation. The milling guide""s pivotal axis is parallel to the vertical axis of the milling assembly. The milling assembly also moves vertically up and down along its axis orthogonal to the milling table and is controlled at a predetermined feed rate to produce a chip load based on the material being shaped. The milling assembly controls the depth of the groove by moving up and down along its vertical axis. The complexity of the apparatus required for performing and controlling geometric machining is thus reduced or minimized.
In one embodiment, a single cutting tool is used for shaping a radial conical groove. In this embodiment, the milling table moves in the programmed arc along the x axis using the y axis motion to generate the arc. The cutting tool is secured to the base unit of the milling assembly by means of the tool holding member and moves up and down along the z axis to control the chip load per pass and the depth of the groove. The milling table also moves along the y axis in a programmed motion to maintain proper alignment with the milling assembly in order to form a conical shaped groove. In this embodiment, the radial arm is radially displaceable relative to its axis of rotation which allows movement of the milling guide along the x axis in a horizontal plane parallel to but noncoplanar with the milling table. Additionally, the radial arm is axially displaceable relative to the post which allows the radial arm to maintain contact with the milling guide as the milling assembly moves up and down along the z axis.
In another embodiment, multiple or ganged cutting tools can be used when shaping a straight sided radial groove. The milling table moves in a programmed arc in a horizontal plane, and the ganged cutting tools are secured in the base unit of the milling assembly and move up and down along the vertical z axis to control the chip load per pass and the depth of the groove. In this embodiment, the radial arm is radially fixed relative to its axis of rotation while a section of the milling assembly moves relative to the arm along a horizontal x axis.
It is accordingly an outstanding object of the present invention to provide improvements in connection with milling apparatus which produces a radial milling motion through the use of a milling guide and a radial arm.
A further object is the provision of milling apparatus which provides a radial motion of the cutting tool combined with machine feed rates and variable speeds to create a shaping action that produces arcuate grooves of varying radii in workpieces depending on the adjustments of the machine components.
Another object is the provision of milling apparatus of the foregoing character wherein a single cutting tool is used for shaping a conical radial groove, and multiple cutting tools can be used for shaping straight-sided radial grooves.
Still a further object of the invention to provide apparatus of the kind mentioned above which produces high machining precision while minimizing the complexity of the apparatus required for performing and controlling workpiece machining.
Yet another object is the provision of milling apparatus of the foregoing character which is efficient in use and promotes a more economical machining of grooves than heretofore possible.
Yet another object is the provision of milling apparatus that allows use of current milling apparatus tables with little modification.